Online spending rose 17 percent on the Monday after Thanksgiving, one of the busiest days of the year for Internet retailers, as tablets and smartphones let customers shop anytime and anywhere.

Consumers spent about $1.46 billion on so-called Cyber Monday, compared with $1.25 billion a year ago, making it the heaviest online spending day in history, research firm ComScore Inc. said Wednesday. U.S. retail e-commerce spending reached $16.4 billion in the first 26 days of the holiday season, a 16 percent increase from the same time last year.

The convenience offered by mobile devices, especially tablets, is boosting sales for online retailers such as and eBay. Consumers are no longer waiting for Black Friday to shop and they're starting as early as Thursday evening, which will help Internet sales reach $43.4 billion this holiday season, or 10 percent of U.S. retail spending, excluding gas, food and cars, according to ComScore.

"Mobile commerce as a whole has clearly gone beyond what it's traditionally been, which is something primarily for the research phase," Clark Fredricksen, vice president at researcher eMarketer Inc., said in an interview. "Tablets are the key driver in terms of the sales element. They've extended the length of the shopping day."

More than 18 percent of shoppers used a mobile device to access a retailer's website on Cyber Monday, an increase of 70 percent over 2011, according to a Nov. 27 report from IBM Corp. Mobile sales almost doubled, making up 13 percent of total Web-based purchases, the company said.

EBay mobile sales volume more than doubled on Cyber Monday, compared with the previous year, and PayPal payment volume nearly tripled, Johnna Hoff, an eBay spokeswoman, said in an e-mail. Consumers worldwide shopped most frequently from 9 a.m. to 10 a.m. Twin Cities time, the company said.

For eBay, Sunday was the biggest mobile shopping day, providing evidence that consumers are using mobile devices to debunk the tradition of splurging most on Black Friday and Cyber Monday.

"Our success on Black Friday and Cyber Monday was surpassed on Sunday when we experienced the biggest mobile transacted volume day of the year, as shoppers continue to embrace an anytime, anywhere mobile shopping experience," Steve Yankovich, eBay's vice president of mobile, said in the e-mail.